Transducer system

ABSTRACT

A circuit for energizing a differential inductor transducer uses rectifier voltage dividers in a balanced bridge circuit.

United States Patent [72] Inventor George Scourtes Detroit, Mich.

[2 l Appl. No. 871,020

[22] Filed Nov. 5, 1969 [45] Patented Nov. 23, 1971 [73] Assignee CoxInstruments Division Lynch Corporation Detroit, Mich.

Original application Oct. 5, 1965, Ser. No. 494,164, now Patent No.3,528,288. Divided and this application Nov. 5, 1969, Ser. No. 871,020

[54] TRANSDUCER SYSTEM 8 Claims, 7 Drawing Figs.

[52] U.S.Cl

[51] Int. Cl G080 19/08 [50] Field of Search 340/199, 196, l95

[56] References Cited UNITED STATES PATENTS 3,046,533 7/1962 Torn340/l99 Primary Examiner-Thomas B. Habecker Attorney-Harness, Dickey andPierce ABSTRACT: A circuit for energizing a differential inductortransducer uses rectifier voltage dividers in a balanced bridge circuit.

PATENTEUH Y 2 WI 3, 623.046

SHEET 1 OF 2 J (3! HiYliN-TOR.

g a gm TRANSDUCER SYSTEM This is a division of Ser. No. 494,164, filedOct. 8, I965, now US. Pat. No. 3,528,288.

This invention generally relates to new and useful improvements intelemetering systems, and more specifically to improvements in atransmitting transducer device for changing rate of flow or pressureinto a signal and further to improvements in an electrical indicatingsystem for producing an output signal in accordance with the relativemovement of an element in a transducer device.

Fluid flow or pressure responsive telemetering systems of the type towhich the present invention is generally directed, have come intogreater widespread use due to increased tolerance requirements in fluidflow or pressure devices, thus increasing the need for highly accuratetelemetering systems over a wide range of flows or pressures. Suchsystems have equal applicability to the flows or liquids or gases orpressures caused by the pumping of the liquid or gases.

A similar need has risen in the area of bidirectional flow or pressuremeters wherein the peak amplitude of fluid flows or pressures in bothdirections may be accurately measured and indicated. One such need for abidirectional telemetering system including a bidirectional transmittingtransducer, involves the situation of a hydraulic pump and hydraulicmotor combination wherein fluid is pumped into and out of the line bymeans of a piston. With the unidirectional metering systems of the priorart, it has become necessary to convert the motor shaft rotation into aconsistent hydraulic flow, in one direction, by means of a valvingapparatus. Thus, an auxiliary line must be provided for use inconjunction with the telemetering system, thereby precluding the use ofthe telemetering system directly in the pumping line,

Accordingly, it is one object of the present invention to provide a newand improved telemetering system for indicating the rate offlow ofafluid or the pressure ofa fluid.

It is a further object of the present invention to provide an improvedtelemetering system which is responsive to a wide range of flows orpressures.

It is still a further object of the present invention to provide animproved telemetering system which is responsive to a wide range offlows or pressures.

It is still a further object of the present invention to provide animproved telemetering system which is bidirectionally responsive bymerely reversing a switch.

It is still a further object of the present invention to provide animproved transducer device for a telemetering system which isautomatically responsive to fluid flows in both directions and isresponsive to pressure, both positive and negative in the latter casevacuum.

It is another object of the present invention to provide an improvedtelemetering system which may be adapted to provide an output inresponse to fluid flows or pressures which is a function of flow orpressure, as for example a logarithmic, linear, or squared output.

It is still a further object of the present invention to provide animproved telemetering system having a transducer device which is freefrom any rotating parts, such as wheels, or moving ball bearings.

A further object of the present invention is to provide an improvedtransducer mechanism for producing an electrical output signal inaccordance with either the amplitude variations of a bidirectional flowor pressure or is capable of producing an output signal in accordancewith a fluid flow or pressure in either direction.

It is still a further object of the present invention to provide animproved transducer device for converting fluid flow or pressure to anelectrical signal which is capable of measuring flow substantially downto zero and up to a very large flow or pressure.

It is still a further object of the present invention to provide asimplified variable orifice, bidirectional transducer device which iscapable of converting fluid flow or pressure to an electrical signal.

It is still another object of the present invention to provide animproved transducer device for converting fluid flow or pressure into anelectrical signal, the transducer device being simple to mount directlyin the fluid flow line or directly on a pressure responsive transducer.

It is still a further object of the present invention to provide animproved transducer device for converting fluid flow or pressure to anelectrical signal which is effectively centered by means which variesits force in a substantially linear relationship with the amount ofdeflection of an armature member.

It is still a further object of the present invention to provide animproved fluid flow or pressure to an electrical signal convertertransducer device which is simple to assemble and extremely accuratelyradially centered within the bore of the transducer device.

It is still a further object of the present invention to provide animproved indicator system.

It is another object of the present invention to provide an improvedindicator system which may be rendered bidirectional by merely actuatinga switch,

It is still a further object of the present invention to provide animproved indicator system utilizing a voltage doubler rectifier andincorporating substantially no amplification elements therein.

It is still a further object of the present invention to provide animproved indicating system wherein a plurality of reference potentialsand a plurality of position sensitive coils are fed from the same sourceof electrical energy.

It is still a further object of the present invention to provide animproved indicating system wherein is provided a simplified referencevoltage zeroing network and a span adjust network, the system furtherbeing provided with a second simplified span adjust network for flows inthe opposite direction or pressures in the opposite direction from thoseindicated by said first circuit.

It is stilla further object of the present invention to provide animproved indicating system wherein the diflerence in voltage between achange in voltage level of each of a plurality of position sensitivecoils and a reference level is fed to a voltage doubling circuit.

It is still another object of the present invention to provide animproved indicator system wherein signal drift in response to change inelectrical characteristics of the system due to temperature changes andthe like, are substantially eliminated.

It is still a further object of the present invention to provide animproved telemetering system which is inexpensive to manufacture,reliable in used and substantially impervious to harmful effects causedby the fluid reacting on the transducer element.

Further objects, features and advantages of the invention will becomeapparent from a consideration of the following drawings wherein:

FIG. I is a perspective view illustrating the improved transducer deviceinstalled in flow sensing relation with a fluid carrying conduit;

FIG. 2 is a cross-sectional view of the transducer device of FIG. I,with the mounting means removed and illustrating the interior portion ofthe transducer device;

FIG. 2a is an elevational view of the diffuser member of FIG. 2;

FIG. 3 is an elevational view of a modified form of the bore andarmature member of FIG. 2;

FIG. 4 is a perspective view illustrating a pressure responsivetransducer device incorporating certain principles of the presentinvention;

FIG. 5 is a cross-sectional view of a further pressure responsivetransducer device and illustrating the interior features thereof; and

FIG. 6 is a schematic diagram of an indicating system incorporatingcertain other principles of the invention, the indicating system beingcapable of being utilized with any form of transducer device, includingthose illustrated in FIGS. 1 to 5.

Referring now to the drawings, particularly to FIGS. 1 and 2, atelemetering system incorporating the principles of the presentinvention is illustrated wherein a flow or pressure transmittingtransducer 10 may be incorporated directly into the line by means of acoupling mechanism 12. The coupling mechanism 12 generally comprises apair of concentrically counterbored plates l4, 16 which are positionedon each end of the flow or pressure line 18 in face-opposing relationwith each other, whereby the counterbored portions are in axialalignment with the axis of the pressure or fluid flow lines 18. The twoface-opposing, counterbored and plate members 12 provide a space intowhich the transducer device 10 may be inserted. Each of the end platesl4, l6 and each end of the transducer device 10 have a pair of matingfaces formed thereon which are capable of being brought into sealingengagement with of the through suitable gasket means disposed betweenthe opposing faces. Thus, a leakproof seal is provided between the fluidflow line 18 and the transducer device 10. A plurality of fastenermembers 22, representativeiy illustrated as nut-bolt assemblies, areprovided on the outer periphery of each of the end plate members 14, 16whereby the tightening of the fastener assemblies 22 brings the matingfaces into sealing engagement with each other. lt is to be understoodthat the opposing faces of plates l4, 16 may be made relatively flat,without a counterbored portion, and the bolts 22 utilized to center thetransducer on the plates l4, 16. Similarly, other forms of connection tothe line 18, as will be discussed in conjunction with the detaileddescription of HO. 2, may be utilized in connecting the transducer tothe pressurized line 18.

The transducer assembly itself generally comprises an outer housing orshroud member 28 formed of magnetic material, which is adapted tosurround a monmagnetic body portion 30 having a pair of peripheralgrooves 32 formed therein which are adapted to receive a pair ofcircularly induction wound coils 34, 36. The interior of the bodyportion 30 is formed with a bore 40 which is adapted to receive anarmature assembly 42 therein. Theamiature assembly 42 generallycomprises a pair of end member 44, 46 which are suitably positioned ateither end of the body portion and serve as diffusers to break up anyflow pattern which may be present in the flow of fluid through the fluidline l8. The two diffusers 44, 46 or end members may be formed ofmagnetic or nonmagnetic material and are interconnected by a nonmagneticshaft member 50 having an armature member 52 slidably retained thereon.The armature member 52 is positioned in the axial center of the bore 40by a pair of opposing spring members 56, 58 which are adapted to engagethe armature member 52 at one end thereof and the diffuser members 44,46 at the respective other ends. The armature member 52 is formed with apair of peripheral guide portions or pilots 60, 62 as are the diffusermembers formed with like circumferential guide portions or pilots 64, 66to suitably support the spring members 56, 58. Thus, the annature member52 is effectively centered on the shaft 50 between the two diffusers 44,46 and is capable of being slidably displaced on the shaft, in onedirection or other, by means of fluid flowing in one or the otherdirection. it will be noted that the spring members 56, 58 arepositioned between the end member 100 and armature 52, and armature 52and end member 102 such that the effective forces of the springs areopposing each other to increase the effective spring rate of thecombination of springs 56, 58. For example, in linear springs havingequal springs rates, the effective spring rate of the combination ofsprings 56, 58 is doubled. The initial force or preload on the armatureat zero flow ore pressure conditions is essentially zero. Thus, therange of the transducer device is greatly increased over conventionaltransducers.

The shroud member 28 is provided with a nipple assembly 70 which isadapted to house a plurality of connections to the coils formed in thegrooves of the body member. The nipple assembly generally includes anannular shaped body portion 72 which may be integrally formed or castwith the shroud member 28 or suitably attached thereto, as by welding.The interior of the body portion 72 is in communication with the grooves32 formed in the body member 30. thereby facilitating the positioning ofa pair of leads 72 therein. A support member 78 is attached to the bodyportion 72, as by screws to form terminals for the leads 74. A connectormember 80 is threaded or otherwise fastened to the body portion andprovides protection for the cable connection to a suitable electricalindicating apparatus. The coiis 34, 36 are normally in series, wherebythe magnetic flux produced by energization of the coils 34, 36 will flowthrough the body member 30, through the magnetic armature member 52 tothe diffuser member 44 in the case of magnetic diffuser 44, and back tothe respective end of the magnetic shroud member 28.

As stated above, diffuser members 44, 46 may be chosen to be fabricatedof magnetic or nonmagnetic material. in the case where the diffuser isformed of magnetic material, the flux path from the coils 34, 36 will bethrough the diffuser members 44, 46 as a low reluctance path. In thissituation, the movement of the armature member varies the reluctance ofthe flux path approximately as a square function of the position of thearmature. However, in the case where the end members 44, 46 are formedof nonmagnetic material, the output signal from coils 34, 36 will varyas a linear function of the position of the armature 52. in this lattercase, the flux path will be through the radial gap between the hub endof the armature member and the body portion 30.

It is to be noted that the movement of the armature member 52 on theshaft 50 due to the increase or decrease of flow through the bore 40will increase or decrease the gap between the armature member 52 an therespective diffuser or end member 44 thereby increasing or decreasingthe reluctance of the magnetic path for the flux produced by the coil.The second coil 36 has a similar path through the left portion of theshroud member 28, the body member 30 at the left portion thereof, thediffuser member 46 in the case of a magnetic diffuser, the variable airgap to the armature member and back to the shroud member. in the casewhere the diffuser is nonmagnetic, the flux path will be through the gapbetween the hub 8] of the annature member 52, as described above. it isto be noted that the change in air gap due to the movement of thearmature member in one direction, will increase the reluctance of one ofthe coils while at the same time decreasing the reluctance of the fluxpath of the other coil. Thus the impedance of one coil is increasedlinearly while the impedance of the opposite coil is decreased linearlyby a corresponding amount.

The interior of the bore has been formed with a constructed flow areaportion 82 which is in mating engagement with a circular knife edge 84formed on the armature member 52. At zero flow, the armature iseffectively centered with the knife edge 84 on the armature contiguousto the reduced flow area portion 82 of the bore. The knife edge on thearmature member is formed by removing portions of the body of thearmature member in a particular configuration or by molding the bore 40in the desired configuration. In the representative example illustrated,the bore is shown to be decreasing linearly, however, it is to beunderstood that any configuration may be utilized to produce a desiredoutput.

For example, an exponential curve or an exponentially decreasing andincreasing flow area will react with the flow to produce an output inthe indicating system which is substantially linear. On the other handif a linear decreasing and increasing flow area is utilized, the outputat the indicating device will be substantially logarithmic. Also, in theevent a smooth bore is utilized, the output will vary as a squarefunction of the flow. Similarly, the armature member has materialremoved from an outer portion thereof to form the knife edge 82, andthis material may be removed in a plurality of configurations. Forexample, the surfaces 86, 88 may be formed in a straight or linearconfiguration, as illustrated in FIG. 2 of the drawings, or anexponential configuration, as illustrated in the modified form 90 of thearmature shown in FIG. 3. Thus with an increase of flow, the floworifice through which the fluid is flowing will vary in either a linearor exponential fashion to produce a logarithmic or linear output,respectively, or as a square output in the case of a smooth bore. Theconfiguration of both the annature member and the bore is symmetricalabout the zero flow point thereby providing a bidirectional indicatingdevice. The flow in one direction will enter the transducer from theright through the apertures 92 formed in the diffuser 44 to impinge onthe right face of the armature 52. The flow then travels through theremainder of the bore 40 after moving the armature 52 to the left, andexits from the transducer through apertures 94 formed in the diffuser46.

Referring specifically to FIG. 3, it is seen that the bore 40 is formedas a smooth cylinder and a variable orifice means 91 inserted thereinhaving a' pair of elongated portions 93, 95 which are adapted to closelyfit the interior diameter of the bore 40 to retain the member 91therein. A central portion is formed with a flow constricting swaggedportion 97 to vary the deflection of the armature 90 in accordance witha particular function offlow.

In F IG. 2, armature member assembly 42 is accurately radi allypositioned in the bore 40 by means of an annular, inwardly facing pairof counterbores 96, 98 formed on the inner surface of the body member30. The counterbores 96, 98 are accurately fonned concentrically withrespect to the axis of the bore thus positioning the center of thediffusers 44, 46 on the axis of the bore. The diffusers 44, 46 include acentral hub portion 100, 102 which are formed with counterboredapertures 104, I06 concentric with the outer periphery of the diffusers44, 46. The inside diameter of the apertures 104, 106 closelyapproximate the outside diameter of the shaft 50 thereby forming a closefit therebetween. The hub portions 100, 102 are provided with internallythreaded bores which are adapted to threadedly engage mating threadedends of the shaft 50. In assembling the armature assembly 42, onediffuser is threaded on the shaft 50 and the first spring, the armatureand then the second spring are successively placed on the shaft 50 inthe order shown and described. The annature assembly thus formed is theninserted into the bore from on end and the remaining diffuser isthreaded onto the shaft from the other end of the bore 40. The diffuseris continuously threaded until the diffusers are inserted into thecounterbores 96, 98 and in binding engagement with the shouldersformedin the bore 40. The binding force is sufficient to retain'the armatureassembly 42 in the bore 40.

As stated above, the mounting assembly I2 may take other forms suitablefor use in pressurized lines, such as line 18. One such form includesremoving the diffuser members 44, 46 from from the counterbored portions96, 98 and forming interior threads on counterbores 96, 98. An elongateddiffuser nipple member formed of solid cylindrical, or stepped stock, isthen threaded into portions 96, 98 by means of exterior threads fonnedtherein, and a portion of the diffusers may project beyond the bodymember 30. The diffuser nipples may then be counterbored at the exteriorends thereof and threaded to receive the threaded end of the pipe 18 anda diffuser may be formed by drilling through the portion of the nipplewhich has not been counterbored. Thus the pipe, diffusers and bore 40are properly aligned. A second modification may take the form of aflange fitting wherein a solid stock is similarly formed in a nipplefitting, as described above. For example, a solid, stepped generallycylindrical stock has a first end threaded on an exterior surfacethereof to threadedly engage mating threads formed on the interior ofportions 96, 98. The portion of the cylinder adjacent the threadedportion may have a larger exterior diameter than the threaded portionand is adapted to slidably receive a radially extending flange memberthereon. The outer end of the nipple is formed with a still largerdiameter portion to retain the flange on the nipple and the flange maybe counterbored to receive the head portion. The head portion is adaptedto coact with the body por tion to retain the flange in position andalso to provide strength to the flange member when it is mated with asecond flange member on the pressurized pipe. The threads on theinterior surface of the counterbored portion are omitted in thissituation due to the fact that the end of the pipe is not threaded.

As stated above, the invention incorporated herein is not restricted toflow type of transducer devices but also may be made to include pressureresponsive transducers including systems wherein a means is provided fortransforming pressure into linear movement, the linear movement beingconnected to a second transducer device which is cable of transformingthe mechanical movement into an electrical signal. In one fonn, thegeneral configuration of the first transducer may take the form of aBourdon tube, or any form of pressure responsive device, and the secondtransducer may take a form which is substantially identical to thatdescribed in conjunction with the flow type of transducer. However, inpressure responsive type transducer, the armature member may be fixedrelative to a shaft, the shaft being slidably mounted in a pair of endmembers which are suitably mounted in the bore in either end of the bodymember and concentric with the bore, or may be slidable mounted on afixed shaft, as described in conjunction with FIG. 2.

Referring now to FIGS. 4 and 5, there is illustrated one preferredembodiment of a pressure responsive transducer assembly which may beutilized with the indicator system illustrated in FIGS. 6. Referringfirst to FIG. 5 and as described in conjunction with the flow situation,a body member 112 is provided with a pair of concentrically wound coilsI14, 116 which set up a pair of flux paths through an armature member l18 and end members 120, 122 whereby the movement of the armature memberincreases the reluctance of one path and decreases the reluctance of theopposite path, as was the case with the fluid responsive transducerassembly 10. It is to be noted that end members 120, 122 may be formedof magnetic or nonmagnetic material in accordance with the desiredoutput results. Accordingly, the impedance of the above mentioned coilsis varied in accordance with the position of the armature within thebore. A pair of opposing centering springs 128, are provided toinitially position the armature within the bore, thus zeroing thearmature 118 within the transducer device 110.

The output of the transducer device is fed through a nipple assembly 134attached to the outer periphery of a shroud member 136 and includes aplurality of conductors 138, 140 in electrical communication with thecoils 114, 116 formed in the body member 112. The induction coils I14,116 are connected in series across a suitable source of alternatingcurrent potential and the voltage drop across each of the coils variesin accordance with the change of reluctance of the respective magneticpaths due to the change in position of the armature member in the boreof the body response to a variation in pressure. Accordingly, for angiven voltage drop or voltage supplied to the coils, the total voltagedrop will be proportioned across each of the coils in accordance withthe reluctance of the respective magnetic paths thereby providing anindication of the relative position of the armature member within thebore.

In the modification illustrated in FIG. 5, the armature 118 is slidablysupported relative to shaft 142 and the shaft is relatively fixed withrespect to the end members 120, 122. A cylindrical portion of frictionmaterial may be positioned to form retaining members I44, 146, tofacilitate the assembly of shaft 142 within end members 120, 122 or endmembers 120, 122 may be threadedly fixed to the shaft 142, as in thecase of FIG. 2. The end members are radially positioned within the boreof the body member 112 by means of concentric grooves 152, 154 formedtherein as described in conjunction with FIGS. 1 to 3. The end members120, 122 are fixed in the grooves by suitable snaprings 156, 158 or anyother fastening means, or merely by the threaded engagement between endmembers 120, 122 and shaft 142. The transducer The transducer of FIG. 5is particularly adapted to measure pressure drops across a valvingmember, orifice or the like wherein one face of the transducer 110 issuitably connected to a tube which is in fluid communication with thepressurized portion on one side of the valve, etc. while the other faceof the transducer is connected to a tube which is in fluid communicationwith the other side of the valve, etc. The connection may be made in anysuitable manner, as for example, with the connectors described above. Asan alternative arrangement, the retaining members 144, 146 may be formedof a relatively frictionless bearing material to permit the shaft 142 tobe freely slidable therein. in this situation, the armature member isfixed relative to the shaft 142 and the shaft-armature assembly isaxially shifted in response to an increase or decrease in pressure.

Referring particularly to FIG. 4, a pressure responsive transducerdevice is illustrated as being connected in pressure responsive relationto a Bourdon tube of pressure responder. It is to be understood thatwhile the subject invention is illustrated and described in conjunctionwith the Bourdon tube type responder, any type of pressure responder maybe utilized to linearly actuate the shaft member 142. Thus, any type oftransducer device which is capable of transforming bidirectional orunidirectional pressure into a linear motion may be utilized to actuatethe shaft 142. It is to be understood that pressure is used genericallyto include both a positive and negative pressure, a pressure or vacuum,respectively.

The responder 170 generally comprises a tubular member 172 which isadapted to be attached to a line, the pressure of which is to bemeasured by means of a connector assembly 174. The other end of thetubular member 172 is interconnected with stand assembly by means of arigid fitting assembly 176 wherein the coupling 174 and fitting assembly176 may take any form common in the art. The upper end of the rigidfitting assembly 176 is provided with a conventional Bourdon tube 180,which is generally of a C" configuration having one end fixed to a blockportion 182 forming a part of the stand assembly 176, and the other end184 thereof, being interconnected with the longitudinally movable shaft142 through a fixed linkage assembly 188. The Bourdon tube is of a typewherein the end 184 is moved outwardly of the transducer device 110 asthe pressure increases and moves inwardly toward the transducer 110 asthe pressure decreases. Similarly, in a vacuum situation, the greaterthe vacuum the more the displacement of the end 184 toward thetransducer device 110.

Accordingly, the shaft member 142 is moved inwardly and outwardly with adecrease and increase in pressure, respectively, to thereby change therelative reluctance of the induction coils 114, 116 contained within thetransducer device 1 10. The linkage assembly maybe of any type, and isrepresentatively illustrated as comprising a plate member [Q which iswelded or otherwise rigidly fastened to the end 184 of tube 180 and acentral portion of the plate member 190 is similarly welded or otherwisefixed to the end of the elongated shaft 142. Accordingly, the up anddown motion of the end 184 is transmitted to the shaft member 142through the linkage assembly 188. The interior of the transducer 110 maytake a similar form to that illustrated in FIG. 5 with the exceptionthat the springs 126, 130 and the end members 120', 122 are eliminatedto reduce the opposition to the movement of shaft 142. Also, armaturemember 118 is fixed relative to shaft 142 and shaft 142 is extended atone end thereof to permit the attachment of the linkage assembly 188. Inthe situation where a large force is developed for a given change inpressure, it may be desirable to retain springs 128, 130 and end members120, 122 to increase the range of the transducer 110.

While certain prior art systems utilize circuitry which is capable ofmeasuring the variation of impedance of a position sensing winding. Theindication system of the present invention incorporates a sensingcircuit which provides an output signal in accordance with the ratio ofimpedances of the plurality of windings on the body member. Thus, avariation in impedance of the sensing coils in response to temperaturechange and the like, will not vary the output signal indicative of theposition of the armature within the bore. Also, the indication system ofthe present invention utilizes a rectified voltage doubler circuit whichprovides the measuring art with a highly responsive direct currentsignal derived from an alternating current source, the direct currentsignal being of suffcient magnitude to actuate an indicating device, asfor exam ple a galvanometer, or the like.

Referring now to FIG. 6, there is illustrated a representativeembodiment of an indicating circuit which is adapted to be utilized inconjunction with the transducer device described in conjunction withFIGS. 1 to S. Particularly, the indicating circuit is provided with aninput source of power by means of a plug 202 which is adapted to beinterconnected with a suitable source of alternating current, as forexample, volt AC. The plug is connected through a pair of switches 204,206 to a constant voltage or voltage regulated transformer 208, whichincludes a primary winding 210, a secondary winding 212 and a coremember 214. The transformer 208 may be of the type such as that soldunder the trade name Sola Transformer."

The output of the transformer 208 is fed through a pair of conductors218, 220 to a transducer circuit 222, the transducer circuit consistingof a pair of series connected inductor windings 224, 226. The inductorwindings 224, 226 correspond to the windings 34, 36 of FIG. 2 or 114,116 ofFlG. 5, and both windings are chosen to have generally the sameelectrical and magnetic characteristics. The windings 224, 226 aremagnetically coupled to a magnetic armature member 230 which ispositioned in flux coupling relation to both of the windings 224, 226.The magnetic member 230 is a schematic representation of the variablemagnetic circuit of FIGS 2 and 5 caused by the bidirectional movement ofthe armature 52 and 118, respectively. The armature 230 is adapted tomoved linearly in a direction parallel to the axis of the coils 224,226. Accordingly, when the armature member 230 is moved downwardly, theimpedance of the winding 224 is lowered and the impedance of the winding22 6 is corresponding raised.

It is to be noted that a constant voltage impress across conductors 218,220, thereby presenting a constant voltage across the series combinationof the windings 224, 226. Thus, the drop across each of the windings224, 226 will be a proportionate share of the total voltage presentacross conductors 216, 220, and is representative of the relativemovement of the armature member 230 across the magnetic path of each ofthe windings. The voltage across conductors 218, 220 is also fed to afirst =balanced voltage divider circuit 234, utilized when the voltageat conductor 218 is positive with respect to conductor 220, asecondbalanced voltage divider circuit 236, which is adapted to be utilizedwhen the voltage at conductor 218 is negative with respect to beutilized when the voltage at conductor 218 is negative with respect toconductor 220, and a voltage doubler bridge circuit 240, which isadapted to provide an indication of the flow or pressure within thesystem.

The balanced voltage divider circuit 234 includes provisions for varyingthe output voltage thereof in such a manner such that the voltage acrossconductors 218 and 220 is exactly halved at the output terminal thereof.Similarly, the second balanced voltage divider circuit 236 also includesprovisions for diving the voltage between conductors 218, 220 andpresenting this divided voltage as an output signal. The voltage doublerbridge circuit 240 includes means for reversing the polarity of theindicating circuit and also further includes means for adjusting thespan of the indicating device contained therein to provide a full scaledeflection at the maximum flow of pressure which is anticipated.

Referring to the first balanced voltage divider circuit 234, the voltageacross conductors 218, 220 is fed through a diode 250, a firstrelatively low impedance resistor 252, a second relatively low impedanceresistor 254, and a second diode 256 all connected in series betweenconductors 218 and 220. A variable impedance, potentiometer circuit isconnected across the series combination of resistors 252, 254 andgenerally comprises a slider 268, a potentiometer arm resistor 260 and apotentiometer resistor 262. in the circuit of the present invention, itis desired to provide a voltage at a node 264 between resistors 252 and254 which is half the voltage between conductors 218 and 220,Accordingly, the slider potentiometer, including resistors 260, 262, maybe varied to vary the upper portion of resistor 262 as compared to thecombination of resistors 254, 260 and the lower portion of 262. Thus,the voltage at node 264 may be varied by varying the position of theslider 268 with respect to the resistor 262.

The second balanced voltage divider circuit 236 is similarly connectedwith a pair of diodes 270, 272 connected in series with a pair ofresistors 274, 276, the resistors 274, 276 and diodes 270, 272 beingconnected across the conductors 218, 220. The second voltage dividercircuit has been illustrated with fixed resistors 274, 276 to set thevoltage at a node 290 with respect to the conductor 220. Accordingly,the voltage divider circuit 234, and particularly the zero resistor 262is utilized to balance the voltage at node 264 to that of node 290.However, a second balancing or zero circuit may be incorporated intodivider circuit 236 to provide additional adjustment of the voltage atnodes 264, 290. Accordingly, the voltage at node 290 will beapproximately half the voltage across conductors 218 and 220.

The output voltages at nodes 264 and 290 are fed to opposite points ofthe bridge circuit 240 and a center tap conductor 294 is connected to anupper node 296 of the bridge 240, the other end of which being connectedto a node 292 between the inductors 224 and 226. A first capacitor 300is connected between nodes 264 and 296 and a second capacitor 302 isconnected between nodes 290 and 296. Thus voltage across capacitors 300and 302 will vary in accordance with the difference in potential betweenthe voltage at nodes 264 and 296 in the case of capacitor 300 and thedifference in voltage between nodes 290 and 296 in the case of capacitor302, as will be more fully explained in conjunction with the descriptionof the operation of the circuit.

A galvanometer type indicating device 306 is connected at one endthereof to a first reversing switch 308 and through a variable spanimpedance 310 to the node 264 and the other end of the indicating device306 is connected to node 290 through a second reversing switch 314 and aconductor 316. The span impedance 310 is made variable to vary theamount of current being fed to the indicating device to provide a fullscale deflection for the maximum amount of flow or pressure which isanticipated, thereby providing a calibration means for the indicatingdevice in accordance with the anticipated rating of the system.

With the reversing switches 308, 314 in the opposite direction, or poledopposite to that shown, a circuit is completed from node 290 through asecond span variable resistor 320, a terminal 322, the arm of reversingswitch 308, the indicating device 306, to the arm of the secondreversing switch 314. With the arm of the reversing switch 314 in theopposite position, that is in contact with a second terminal 324, theindicating device 306 is connected to the node 264 through a conductor328. Each of the resistors 310 and 320 have been provided with a slidingarm 330, 332 to vary the impedances of the resistors 310, 320 and also apair of diodes 334, 336 have been connected in oppositely poled, shuntrelation to the indicating device 306 to provide protection for theindicating device 306.

In operation and assuming that the reversing switches 308, 314 are inthe position shown, the system is initially calibrated with zero flowthrough the meter. It is further 44 assumed that the armature 230 hasbeen exactly centered between the inductors 22 4 and 226 at a no-flowcondition. Accordingly, the switches 204 and 206 are closed, thusapplying a voltage between conductors 218 and 220 and for purposes ofexample, it is assumed that the voltage across conductors 218, 220 hasbeen lowered to approximately 6-volts, alternating current, due to thestep down transformer 208. For purposes of simplicity, the conversionbetween alternating current and direct current will be assumed to beequal and the 3-volt volt direct current potential at the nodes 264, 290is assumed to be one-half of the potential across the conductors 218,220.

Accordingly, a 6 volt potential is impressed across conductors 218, 220and accordingly across the series combination of the diodes 250, 256 andthe balanced voltage divider circuit 234 and similarly the seriescombination of diodes 270, 272 and the balanced voltage divider 236. Itis to be understood that the voltage divider circuit 234 is utilizedduring what is assumed to be the positive half cycle or whereinconductor 218 is positive with respect to the conductor 220, and thevoltage divider circuit 236 is utilized during the correspondingnegative half cycle or when conductor 220 is positive as compared toconductor 218. Accordingly, with zero current flow through the meter,thereby permitting armature 230 to assume the null or zero position, themeter 306 should read zero due to the fact that the average pulsating DCvoltage at a node 264 is approximately 3-volts and the average pulsatingDC voltage at node 290 is also approximately 3-volts. However, it isimportant to note that the voltages at nodes 264 and 240 are identical.lf these voltages are not identical, the slider 268 may becorrespondingly adjusted to vary the voltage at node 264 to thereby zerothe meter indicating device 306.

With the circuit initially at rest and with the balanced voltage dividercircuit circuit 234 adjusted to the half way position wherein thevoltages at nodes 264 and 290 are exactly equal, the switches 204 and206 are closed, thereby permitting the first half wave to flow throughthe circuit,. Accordingly, the upper end of inductor winding 224 ispositive with respect to the center tap node 292 and the node 292 ispositive with respect to the conductor 220, assuming that the armaturedevice 230 has been sufi'iciently lowered to cause the lower inductor226 to drop twice the amount of voltage available between conductors 218and 220 as compared to the voltage dropped across inductor 224.Accordingly, the voltage across inductor 226 will be approximately 4volts while the voltage across inductor 224 will be approximately 2volts. The center tap voltage at node 292 will be at approximately 4 ascompared to the 6-volts at conductor 218 when measured from conductor220, and this 4-volt potential will be fed to node 296.

It has already been stated that the voltage at node 264 is at 3-voltsthereby providing a l-volt drop across capacitor 300 to charge thecapacitor plus to minus in a direction between nodes 264 and 296 inaccordance with the upper polarity illustrated in parenthesis on thedrawing. The same 4-volt potential applied at node 296 is applied crosscapacitor 302. However, the diodes 270, 272 are back biased to precludethe charging of capacitor 302. However, on the second half cycle, thenegative half cycle, the diodes 270 and 272 will be forwarded biased toestablish a 3-volt potential at node 290 and the voltage at node 296will assume a 4-volt potential with respect to the positive conductor220. Accordingly, the 4-volt potential at node 292 is fed by means ofconductor 294 to the node 296, and with the node 290 at 3-voltpotential, the capacitor 302 will be charged to l-volt, with the upperpolarity illustrated in the drawing. Accordingly, the capacitors 300,302 are charged at l volt each, in accordance with the polarityillustrated, by the first full wave cycle impressed on conductors 218,220.

As is seen from the foregoing description, each of the capacitors 300,302 is charged with the difierences between the voltage at node 296' andeach of nodes 264, 290. Accordingly, the sum of the voltages acrosscapacitors 300, 302 is impressed across the meter 306 to provide anoutput reading which is indicative of the charge on the capacitors. ltwill be noted that the net voltage across the meter 306 is double thedifference signal, thus providing the voltage doubling effect. Theparticular parameters chosen for each charging circuit are typically ofa low impedance to provide the full difference signal across thecapacitors. Contrariwise, the discharge circuit through the meter is ofa high impedance to maintain a substantial portion of the charge on thecapacitors, and any discharging will be resupplied on a subsequentcycle. In this way, the capacitors act as a transfer agent for thecharge from the coils to the meter.

When the second positive half cycle is impressed on conductors 218, 220,the voltage at node 292 will again rise to a 4- volt potential ascompared to the potential at conductor 220, this 4-volt potential beingfed by conductor 294 to the node 296. Accordingly, with a 4-voltpotential at node 202 and with the capacitor 302 charge negative topositive between nodes 290 and 296, current will flow from node 264,through resistor 310, slider 330 combination, reversing switch 308,indicating device 306, reversing switch 314, conductor 3l6, node 290,through a second l-volt potential across capacitor 302 to node 296. itwill be noted that upon the discharge of capacitor 302 due to the flowof current in the opposite direction through the capacitor, thecapacitor 302 gives up its charge to provide the second volt potential,and the capacitor 302 is charged in an opposite direction, or plus tominus as current flows from node 290 to 296. This polarity isillustrated in parenthesis in the drawing. According, a 2-volt potentialhas been impressed across indicating meter 306, the 2-volt potentialbeing double the difference between input nodes 296 and 264.

On the negative half cycle, the conductor 220 becomes positive and node202 assumes a 4-volt potential, the 4-volt potential being fed to node296 by means of conductor 294. With the 4-volt potential at node 296,current will flow from node 296 through capacitor 300, which is chargedminus to plus, to add an additional volt to the signal, through node264, resistor-slider arm combination 330, 310, reversing switch 308,indicating device 306, reversing switch 314, conductor 316 to node 290,which is at a 3-volt potential or l-volt less than the potential at node296. Accordingly, a second 2-volt potential is presented to indicatingdevice 306 and the current flow therethrough is in the same direction aswas the current flow through the indicating device during the positivehalf cycle. This operation is continued thereby giving a constant outputindication at meter 306 until such time as the armature 230 is moved toa new position.

It will be noted from the above discussion that each cycle of currentflow is through resistor 310, slider arm 330 combination. Accordingly,the maximum flow, which is desired to be measured by the systemillustrated, may be passed through or the maximum pressure may beimpressed on the transducer device 222, thereby moving the slug orarmature 230 to its maximum deflection position. Accordingly, withmaximum flow or pressure being impressed on the armature member 230, theeffective resistance presented by resistor 310, slider 330 combinationto the flow of current through the meter may be adjusted such that themeter will provide maximum deflection for maximum movement of thearmature member 230. Accordingly, if the meter is reading below themaximum, the effective resistance of the span resistor 310 may bedecreased and contrariwise, if the meter is reading high, the effectiveresistance of the span resistor 310 may be increased.

As was stated above, the reversing switches 310, 314 have been providedin the event a reverse flow or pressure is impressed on the armaturedevice 230. Accordingly, if the armature is moved in a directionopposite to that described above, the switches 308, 314 are reversedwhereby the annatures are in contact with the terminals 322 and 324. Inthe event it is desired to calibrate the indicating circuit in thereverse direction, the reversing switches are switched into contact withterminals 322 and 324 and the effective resistance of the span resistor320 is adjusted to give maximum flow of maximum deflection of the meter306 for maximum movement of the armature member 230. It will be notedthat the current will flow through the meter in the same direction forthe opposite flow or pressure in the same direction as did current flowthrough the meter 306 in the direction described above.

While it will be apparent that the preferred embodiments of theinvention disclosed are well calculated to fulfill the objects abovestated, it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the properscope or fair meaning of the subjoined claims We claim:

1. in combination with a bidirectional transducer for converting avarying characteristic of a fluid into mechanical movement having asupport member, first and second series connected flux producing coilsmounted on the support member and an armature member supported in theflux path of the flux coils and relatively movable with respect theretoin response to the varying characteristic and producing a signal, themovement of the armature in one direction increasing the reluctance ofsaid first coil flux path and correspondingly decreasing the reluctanceof said second coil flux path, energy means for energizing the first andsecond coils with a source of alternating current potential andproducing a voltage drop across each of said first and second coils inaccordance with the position of the armature means, the improvementcomprising first rectifying voltage divider means connected to saidenergy means for producing a first unidirectional reference from a firsthalf wave of the alternating current potential, second rectifyingvoltage divider means connected to said energy means for producing asecond unidirectional reference voltage from a second half wave of thealternating current potential, and means for doubling the magnitude ofthe signal comprising the difference in voltage between the voltage dropacross said first coil during the first half wave and said firstreference signal and a second signal comprising the difference involtage between the voltage drop across said second coil during thesecond half wave and said second reference signal and indicating meansresponsive to the successive first and second doubled signals forindicating the fluid characteristic.

2. The invention of claim 1 wherein said first and second rectifiervoltage divider means includes first and second series connectedimpedance means connected across the source of energy, third impedancemeans connected in shunt relation to said first and second impedancemeans, and means connected to a point between said first and secondimpedance means and variably connected to said third impedance means forvarying the effective ratio of a combination of said first impedancemeans and a first preselected portion of said third impedance means ascompared to a combination of said second impedance means and a secondpreselected portion of said third impedance means.

3. In combination with a bidirectional transducer for converting avarying characteristic of a fluid into mechanical movement having asupport member, first and second series connected flux producing coilsmounted on the support member and an armature member supported in theflux path of the flux coils and relatively movable with respect theretoin response to the varying characteristic, the movement of the armaturein one direction increasing the reluctance of said first coil flux pathand correspondingly decreasing the reluctance of said second coil fluxpath and the movement of the armature in an opposite directiondecreasing the reluctance of the first coil flux path and increasing thereluctance of the second coil flux path, and energy means for energizingthe first and second coils with a source of alternating currentpotential and producing a voltage drop across each of said first andsecond coils in accordance with the position of the armature means, theimprovement comprising first rectifying voltage divider means connectedto said energy means for producing a first unidirectional reference froma first half wave of the alternating current potential, secondrectifying voltage divider means connected to said energy means forproducing a second unidirectional reference voltage from a second halfwave of the alternating current potential, and means for doubling themagnitude of a first signal comprising the difference in voltage betweenthe voltage drop across said first coil during the first half wave andsaid first reference signal and a second signal comprising thedifierence in voltage between the voltage drop across said second coilduring the second half wave and said second reference signal, includingfirst storage means charged during said first half wave and dischargedin series with said first signal during said second half wave, secondstorage means charged during said second half wave and discharged inseries with said first signal during said first half wave, indicatingmeans responsive to the successive first and second doubled signals forindicating the fluid characteristic.

4. The invention of claim 3 wherein said first and second rectifiervoltage divider means includes first and second series connectedimpedance means connected across the source of energy, third impedancemeans connected in shunt relation to said first and second impedancemeans, and means connected to a point between said first and secondimpedance means and variably connected to said third impedance means forvarying the effective ratio of a combination of said first impedancemeans and a first preselected portion of said third impedance means ascompared to a combination of said second impedance means and a secondpreselected portion of said third impedance means.

5. A bidirectional telemetering system for converting a varyingcharacteristic of a fluid into an indication of the signal comprisingfirst and second series connected flux producing coils, an armaturemember supported in the flux path of the flux coils and relativelymovable with respect thereto in response to the varying characteristic,the movement of the armature in one direction increasing the reluctanceof said first coil flux path and correspondingly decreasing thereluctance of said second coil flux path, energy means for energizingthe first and second coils with a source of alternating currentpotential and producing a voltage drop across each of said first andsecond coils in accordance with the position of said annature means, theimprovement comprising first rectifying voltage divider means connectedto said energy mearis for producing a first unidirectional referencefrom a first half wave of the alternating current potential, secondrectifying voltage divider means connected to said energy means forproducing a second unidirectional reference voltage from a second halfwave of the alternating current potential, and means for doubling themagnitude of a first signal comprising the difference in voltage betweenthe voltage drop across said first coil during the first half wave andsaid first reference signal and a second signal comprising thedifference in voltage between the voltage drop across said second coilduring the second half wave and said second reference signal, andindicating means responsive to the successive first and second doubledsignals for indicating the fluid characteristic.

6. In combination with a bidirectional telemetering system for conveninga varying characteristic ofa fluid into an indication of the signalcomprising first and second series connected flux producing coils, anarmature member supported in the flux path of the flux coils andrelatively movable with respect thereto in response to the varyingcharacteristic, the movement of the armature in one direction increasingthe reluctance of said first coil flux path and correspondinglydecreasing the reluctance of said second coil flux path and the movementof the armature in an opposite direction decreasing the reluctance ofthe first coil flux path and increasing the reluctance of the secondcoil flux path, energy means for energizing the first and second coilswith a source of alternating current potential and producing a voltagedrop across each of said first and second coils in accordance with theposition of said armature means, the improvement comprising firstrectifying voltage divider means connected to said energy means forproducing a first unidirectional reference from a first half wave of thealternating current potential, second rectifying voltage divider meansconnected to said energy means for producing a second unidirectionalreference voltage from a second half wave of the alternating currentpotential, and means for doubling the magnitude of a first signalcomprising the difference in voltage between the voltage drop acrosssaid first coil during the first half wave and said first referencesignal and a second signal comprising the difference in voltage betweenthe voltage drop across said second coil during the second half wave andsaid'second reference signal, including first storage means chargedduring said first half wave and discharged in series with said firstsignal during said second half wave, second storage means charged duringsaid second half wave and discharged in series with said first signalduring said first half wave, and indicating means responsive to thesuccessive first and second doubled signals for indicating the fluidcharacteristic.

7. A metering system for indicating the ratio of change of the impedanceof a first and second series connected flux producing coils, an armaturemember supported in the flux path of the flux coils and relativelymovable with respect thereto to vary the ratio of the impedances andenergy means for energizing the first and second coils with a source ofalternating current potential and producing a voltage drop across eachof said first and second coils in accordance with the position of thearmature means, the system comprising first rectifying voltage dividermeans connected to the energy means for producing a first unidirectionalreference from a first half wave of the alternating current potential,second rectifying voltage divider means connected to the energy meansfor producing a second unidirectional reference voltage from a secondhalf wave of the alternating current potential, and means for doublingthe magnitude of a first signal comprising the difference in voltagebetween the voltage drop across the first coil during the first halfwave and said first reference signal and a second signal comprising thedifference in voltage between the voltage drop across the second coilduring the second half wave and said second reference signal, includingfirst storage means charged during the first half wave and discharged inseries with said first signal during the second half wave, secondstorage means charged during the second half wave and discharged inseries with said first signal during the first half wave, and indicatingmeans responsive to the successive first and second doubled signals forindicating the fluid characteristic.

8. A metering system for indicating the ratio of change of theimpedances of a first and second series connected flux producing coils,an armature member supported in the flux path of the flux coils andrelatively movable with respect thereto to vary the ratio of theimpedance, the movement of the armature in one direction increasing thereluctance of said first coil flux path and correspondingly decreasingthe reluctance of said second coil flux path and the movement of thearmature in an opposite direction decreasing the reluctance of the firstcoil flux path and increasing the reluctance of the second coil fluxpath, and energy means for energizing the first and second coils with asource of alternating current potential and producing a voltage dropacross each of said first and second coils in accordance with theposition of the annature means, the system comprising first rectifyingvoltage divider means connected to the energy means for producing afirst unidirectional reference from a first half wave of the alternatingcurrent potential, second rectifying voltage divider means connected tothe energy means for producing a second unidirectional reference voltagefrom a second half wave of the alternating current potential, and meansfor doubling the magnitude of a first signal comprising the differencein voltage between the voltage drop across the first coil during thefirst half wave and said first reference signal and a second signalcomprising the difference in voltage between the voltage drop across thesecond coil during the second half wave and said second referencesignal, including first storage means charged during the first half waveand discharged in series with said first signal during the first halfwave, said first and second storage means being oppositely chargedduring the respective discharge portion of the wave to a potential equalto the respective first and second signal, and indicating meansresponsive to the successive first and second doubled signals forindicating the fluid characteristic.

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1. In combination with a bidirectional transducer for converting a varying characteristic of a fluid into mechanical movement having a support member, first and second series connected flux producing coils mounted on the support member and an armature member supported in the flux path of the flux coils and relatively movable with respect thereto in response to the varying characteristic and producing a signal, the movement of the armature in one direction increasing the reluctance of said first coil flux paTh and correspondingly decreasing the reluctance of said second coil flux path, energy means for energizing the first and second coils with a source of alternating current potential and producing a voltage drop across each of said first and second coils in accordance with the position of the armature means, the improvement comprising first rectifying voltage divider means connected to said energy means for producing a first unidirectional reference from a first half wave of the alternating current potential, second rectifying voltage divider means connected to said energy means for producing a second unidirectional reference voltage from a second half wave of the alternating current potential, and means for doubling the magnitude of the signal comprising the difference in voltage between the voltage drop across said first coil during the first half wave and said first reference signal and a second signal comprising the difference in voltage between the voltage drop across said second coil during the second half wave and said second reference signal and indicating means responsive to the successive first and second doubled signals for indicating the fluid characteristic.
 2. The invention of claim 1 wherein said first and second rectifier voltage divider means includes first and second series connected impedance means connected across the source of energy, third impedance means connected in shunt relation to said first and second impedance means, and means connected to a point between said first and second impedance means and variably connected to said third impedance means for varying the effective ratio of a combination of said first impedance means and a first preselected portion of said third impedance means as compared to a combination of said second impedance means and a second preselected portion of said third impedance means.
 3. In combination with a bidirectional transducer for converting a varying characteristic of a fluid into mechanical movement having a support member, first and second series connected flux producing coils mounted on the support member and an armature member supported in the flux path of the flux coils and relatively movable with respect thereto in response to the varying characteristic, the movement of the armature in one direction increasing the reluctance of said first coil flux path and correspondingly decreasing the reluctance of said second coil flux path and the movement of the armature in an opposite direction decreasing the reluctance of the first coil flux path and increasing the reluctance of the second coil flux path, and energy means for energizing the first and second coils with a source of alternating current potential and producing a voltage drop across each of said first and second coils in accordance with the position of the armature means, the improvement comprising first rectifying voltage divider means connected to said energy means for producing a first unidirectional reference from a first half wave of the alternating current potential, second rectifying voltage divider means connected to said energy means for producing a second unidirectional reference voltage from a second half wave of the alternating current potential, and means for doubling the magnitude of a first signal comprising the difference in voltage between the voltage drop across said first coil during the first half wave and said first reference signal and a second signal comprising the difference in voltage between the voltage drop across said second coil during the second half wave and said second reference signal, including first storage means charged during said first half wave and discharged in series with said first signal during said second half wave, second storage means charged during said second half wave and discharged in series with said first signal during said first half wave, indicating means responsive to the successive first and second doubled signals for indicating the fluid characteristic.
 4. The invention of claim 3 wherein said first and second rectifier voltage divider means includes first and second series connected impedance means connected across the source of energy, third impedance means connected in shunt relation to said first and second impedance means, and means connected to a point between said first and second impedance means and variably connected to said third impedance means for varying the effective ratio of a combination of said first impedance means and a first preselected portion of said third impedance means as compared to a combination of said second impedance means and a second preselected portion of said third impedance means.
 5. A bidirectional telemetering system for converting a varying characteristic of a fluid into an indication of the signal comprising first and second series connected flux producing coils, an armature member supported in the flux path of the flux coils and relatively movable with respect thereto in response to the varying characteristic, the movement of the armature in one direction increasing the reluctance of said first coil flux path and correspondingly decreasing the reluctance of said second coil flux path, energy means for energizing the first and second coils with a source of alternating current potential and producing a voltage drop across each of said first and second coils in accordance with the position of said armature means, the improvement comprising first rectifying voltage divider means connected to said energy means for producing a first unidirectional reference from a first half wave of the alternating current potential, second rectifying voltage divider means connected to said energy means for producing a second unidirectional reference voltage from a second half wave of the alternating current potential, and means for doubling the magnitude of a first signal comprising the difference in voltage between the voltage drop across said first coil during the first half wave and said first reference signal and a second signal comprising the difference in voltage between the voltage drop across said second coil during the second half wave and said second reference signal, and indicating means responsive to the successive first and second doubled signals for indicating the fluid characteristic.
 6. In combination with a bidirectional telemetering system for converting a varying characteristic of a fluid into an indication of the signal comprising first and second series connected flux producing coils, an armature member supported in the flux path of the flux coils and relatively movable with respect thereto in response to the varying characteristic, the movement of the armature in one direction increasing the reluctance of said first coil flux path and correspondingly decreasing the reluctance of said second coil flux path and the movement of the armature in an opposite direction decreasing the reluctance of the first coil flux path and increasing the reluctance of the second coil flux path, energy means for energizing the first and second coils with a source of alternating current potential and producing a voltage drop across each of said first and second coils in accordance with the position of said armature means, the improvement comprising first rectifying voltage divider means connected to said energy means for producing a first unidirectional reference from a first half wave of the alternating current potential, second rectifying voltage divider means connected to said energy means for producing a second unidirectional reference voltage from a second half wave of the alternating current potential, and means for doubling the magnitude of a first signal comprising the difference in voltage between the voltage drop across said first coil during the first half wave and said first reference signal and a second signal comprising the difference in voltage between the voltage drop across said second coil during the second half wave and said second reference signal, including first storage means charged during said first half wave and dischArged in series with said first signal during said second half wave, second storage means charged during said second half wave and discharged in series with said first signal during said first half wave, and indicating means responsive to the successive first and second doubled signals for indicating the fluid characteristic.
 7. A metering system for indicating the ratio of change of the impedance of a first and second series connected flux producing coils, an armature member supported in the flux path of the flux coils and relatively movable with respect thereto to vary the ratio of the impedances and energy means for energizing the first and second coils with a source of alternating current potential and producing a voltage drop across each of said first and second coils in accordance with the position of the armature means, the system comprising first rectifying voltage divider means connected to the energy means for producing a first unidirectional reference from a first half wave of the alternating current potential, second rectifying voltage divider means connected to the energy means for producing a second unidirectional reference voltage from a second half wave of the alternating current potential, and means for doubling the magnitude of a first signal comprising the difference in voltage between the voltage drop across the first coil during the first half wave and said first reference signal and a second signal comprising the difference in voltage between the voltage drop across the second coil during the second half wave and said second reference signal, including first storage means charged during the first half wave and discharged in series with said first signal during the second half wave, second storage means charged during the second half wave and discharged in series with said first signal during the first half wave, and indicating means responsive to the successive first and second doubled signals for indicating the fluid characteristic.
 8. A metering system for indicating the ratio of change of the impedances of a first and second series connected flux producing coils, an armature member supported in the flux path of the flux coils and relatively movable with respect thereto to vary the ratio of the impedance, the movement of the armature in one direction increasing the reluctance of said first coil flux path and correspondingly decreasing the reluctance of said second coil flux path and the movement of the armature in an opposite direction decreasing the reluctance of the first coil flux path and increasing the reluctance of the second coil flux path, and energy means for energizing the first and second coils with a source of alternating current potential and producing a voltage drop across each of said first and second coils in accordance with the position of the armature means, the system comprising first rectifying voltage divider means connected to the energy means for producing a first unidirectional reference from a first half wave of the alternating current potential, second rectifying voltage divider means connected to the energy means for producing a second unidirectional reference voltage from a second half wave of the alternating current potential, and means for doubling the magnitude of a first signal comprising the difference in voltage between the voltage drop across the first coil during the first half wave and said first reference signal and a second signal comprising the difference in voltage between the voltage drop across the second coil during the second half wave and said second reference signal, including first storage means charged during the first half wave and discharged in series with said first signal during the second half wave, second storage means charged during the second half wave and discharged in series with said first signal during the first half wave, said first and second storage means being oppositely charged during the respective discharge portion of the wave to a potential equal to the respective first And second signal, and indicating means responsive to the successive first and second doubled signals for indicating the fluid characteristic. 